Switch from type II to I Fas/CD95 death signaling on in vitro culturing of primary hepatocytes

Fas/CD95-induced apoptosis of hepatocytes in vivo proceeds through the so-called type II pathway, requiring the proapoptotic BH3-only Bcl-2 family member Bid for mitochondrial death signaling. Consequently, Bid-deficient mice are protected from anti-Fas antibody injection induced fatal hepatitis. We report the unexpected finding that freshly isolated mouse hepatocytes, cultured on collagen or Matrigel, become independent of Bid for Fas-induced apoptosis, thereby switching death signaling from type II to type I. In such in vitro cultures, Fas ligand (FasL) activates caspase-3 without Bid cleavage, Bax/Bak activation or cytochrome c release, and neither Bid ablation nor Bcl-2 overexpression is protective. The type II to type I switch depends on extracellular matrix adhesion, as primary hepatocytes in suspension die in a Bid-dependent manner. Moreover, the switch is specific for FasL-induced apoptosis as collagen-plated Bid-deficient hepatocytes are protected from tumor necrosis factor alpha/actinomycin D (TNFalpha/ActD)-induced apoptosis. Conclusion: Our data suggest a selective crosstalk between extracellular matrix and Fas-mediated signaling that favors mitochondria-independent type I apoptosis induction.

Cytotoxic diacetylenic spiroketal enol ethers from Plagius flosculosus

Three new diacetylenic spiroketal enol ethers named flosculins A (1), B (2), and C (3), along with five known compounds (4-8) of the same structural class, were isolated from the leaves of Plagius flosculosus. The structures were deduced by extensive 1D and 2D NMR spectroscopy and mass spectrometry. All isolated compounds exhibited significant cytotoxic activity against leukemia cells (Jurkat T and HL-60). Compounds 5-8 induced apoptosis in HL-60 cells with corresponding IC(50) values ranging from 4 to 6 microM.

Effects of Toll-like receptor 2 agonist Pam(3)CysSK(4) on inflammation and brain damage in experimental pneumococcal meningitis

TLR2 signaling participates in the pathogenesis of pneumococcal meningitis. In infant rats, the TLR2 agonist Pam(3)CysSK(4) was applied intracisternally (0.5 microg in 10 microl saline) alone or after induction of pneumococcal meningitis to investigate the effect of TLR2 activation on cerebrospinal fluid (CSF) inflammation and hippocampal apoptosis. A dose effect of Pam(3)CysSK(4) on apoptosis was investigated by intracisternal application of 0.5 microg in 10 microl saline and 40 microg in 20 microl saline. Pam(3)CysSK(4) neither induced apoptosis in sham-operated mice nor aggravated apoptosis in acute infection. However, Pam(3)CysSK(4) induced pleocytosis, TNF-alpha and MMP-9 in CSF in sham-infection but not during acute meningitis. We conclude that TLR2 signaling triggered by Pam(3)CysSK(4) at a dosage capable to induce a neuroinflammatory response does not induce hippocampal apoptosis in the infant rat model of experimental pneumococcal meningitis.

Tumor Regression Grading of Gastrointestinal Carcinomas after Neoadjuvant Treatment

Multimodal therapy concepts have been successfully implemented in the treatment of locally advanced gastrointestinal malignancies. The effects of neoadjuvant chemo- or radiochemotherapy such as scarry fibrosis or resorptive changes and inflammation can be determined by histopathological investigation of the subsequent resection specimen. Tumor regression grading (TRG) systems which aim to categorize the amount of regressive changes after cytotoxic treatment mostly refer onto the amount of therapy induced fibrosis in relation to residual tumor or the estimated percentage of residual tumor in relation to the previous tumor site. Commonly used TRGs for upper gastrointestinal carcinomas are the Mandard grading and the Becker grading system, e.g., and for rectal cancer the Dworak or the Rödel grading system, or other systems which follow similar definitions. Namely for gastro-esophageal carcinomas these TRGs provide important prognostic information since complete or subtotal tumor regression has shown to be associated with better patient's outcome. The prognostic value of TRG may even exceed those of currently used staging systems (e.g., TNM staging) for tumors treated by neoadjuvant therapy. There have been some limitations described regarding interobserver variability especially in borderline cases, which may be improved by standardization of work up of resection specimen and better training of histopathologic determination of regressive changes. It is highly recommended that TRG should be implemented in every histopathological report of neoadjuvant treated gastrointestinal carcinomas. The aim of this review is to disclose the relevance of histomorphological TRG to accomplish an optimal therapy for patients with gastrointestinal carcinomas.

THE ROLE OF PLATELETS IN OVARIAN CARCINOMA

Platelets represent one of the largest storage pools of angiogenic and oncogenic growth factors in the human body. The observation that thrombocytosis (platelet count >450,000/uL) occurs in patients with solid malignancies was made over 100 years ago. However, the clinical and biological implications as well as the underlying mechanism of paraneoplastic thrombocytosis associated with ovarian carcinoma remains unknown and were the focus of the current study. Following IRB approval, patient data were collected on 619 patients from 4 U.S. centers and used to test associations between platelet count at initial diagnosis, clinicopathologic factors, and outcome. In vitro effects of plasma-purified platelets on ovarian cancer cell proliferation, docetaxel-induced apoptosis, and migration were evaluated using BrdU-PI flow cytometric and two-chamber chemotaxis assays. In vivo effects of platelet depletion on tumor growth, proliferation, apoptosis, and angiogenesis were examined using an anti-platelet antibody (anti-mouse glycoprotein 1ba, Emfret) to reduce platelets by 50%. Complete blood counts and number of mature megakaryocytes in the spleen and bone marrow were compared between control mice and ovarian cancer-bearing mice. Plasma levels of key megakaryo- and thrombopoietic factors including thrombopoietin (TPO), IL-1a, IL-3, IL-4, IL-6, IL-11, G-CSF, GM-CSF, stem cell factor, and FLT-3 ligand were assayed in a subset of 150 patients at the time of initial diagnosis with advanced stage, high grade epithelial ovarian cancer using immunobead-based cytokine profiling coupled with the Luminex® xMAP platform. Plasma cytokines significantly associated with thrombocytosis in ovarian cancer patients were subsequently evaluated in mouse models of ovarian cancer using ELISA immunoassays. The results of human and mouse plasma cytokine profiling were used to inform subsequent in vivo studies evaluating the effect of siRNA-induced silencing of select megakaryo- and thrombopoietic cytokines on paraneoplastic thrombocytosis. Thirty-one percent of patients had thrombocytosis at initial diagnosis. Compared to patients with normal platelet counts, women with thrombocytosis were significantly more likely to have advanced stage disease (p<0.001) and poor median progression-free (0.94 vs 1.35 years, p<0.001) and overall survival (2.62 vs 4.65 years, p<0.001). On multivariate analysis, thrombocytosis remained an independent predictor of decreased overall survival. Our analysis revealed that thrombocytosis significantly increases the risk of VTE in ovarian cancer patients and that thrombocytosis is an independent predictor of increased mortality in women who do develop a blood clot. Platelets increased ovarian cancer cell proliferation and migration by 4.1- and 2.8-fold (p<0.01), respectively. Platelets reduced docetaxel-induced apoptosis in ovarian cancer cells by 2-fold (p<0.001). In vivo, platelet depletion reduced tumor growth by 50%. Staining of in vivo specimens revealed decreased tumor cell proliferation (p<0.001) and increased tumor and endothelial cell apoptosis (p<0.01). Platelet depletion also significantly decreased microvessel density and pericyte coverage (p<0.001). Platelet counts increase by 31-130% in mice with invasive ovarian cancer compared to controls (p<0.01) and strongly correlate with mean megakaryocyte counts in the spleen and bone marrow (r=0.95, p<0.05). Plasma levels of TPO, IL-6, and G-CSF were significantly increased in ovarian cancer patients with thrombocytosis. Plasma levels of the same cytokines were found to be significantly elevated in orthotopic mouse models of ovarian cancer, which consistently develop paraneoplastic thromocytosis. Silencing TPO, IL-6, and G-CSF significantly abrogated paraneoplastic thrombocytosis in vivo. This study provides new understanding of the clinical and biological significance of paraneoplastic thrombocytosis in ovarian cancer and uncovers key humoral factors driving this process. Blocking the development of paraneoplastic thrombocytosis and interfering with platelet-cancer cell interactions could represent novel therapeutic strategies.

ROLE OF GSH METABOLISM IN MEDIATING STROMAL-LEUKEMIA INTERACTION AND PROMOTING CELL SURVIVAL AND DRUG RESISTANCE IN CHRONIC LYMPHOCYTIC LEUKEMIA

Chronic lymphocytic leukemia (CLL) is the most common adult leukemia in the western countries. The interaction between CLL cells and the bone marrow stromal environment is thought to play a major role in promoting the leukemia cell survival and drug resistance. My dissertation works proved a novel biochemical mechanism by which the bone marrow stromal cells exert a profound influence on the redox status of primary CLL cells and enhance their ability to sustain oxidative stress and drug treatment. Fresh leukemia cells isolated from the peripheral blood of CLL patients exhibited two major redox alterations when they were cultured alone: a significant decrease in cellular glutathione (GSH) and an increase in basal ROS levels. However, when cultured in the presence of bone marrow stromal cells, CLL cells restored their redox balance with an increased synthesis of GSH, a decrease in spontaneous apoptosis, and an improved cell survival. Further study showed that CLL cells were under intrinsic ROS stress and highly dependent on GSH for survival, and that the bone marrow stromal cells promoted GSH synthesis in CLL cells through a novel biochemical mechanism. Cysteine is a limiting substrate for GSH synthesis and is chemically unstable. Cells normally obtain cysteine by uptaking the more stable and abundant precursor cystine from the tissue environment and convert it to cysteine intracellularly. I showed that CLL cells had limited ability to take up extracellular cystine for GSH synthesis due to their low expression of the transporter Xc-, but had normal ability to uptake cysteine. In the co-culture system, the bone marrow stromal cells effectively took up cystine and reduced it to cysteine for secretion into the tissue microenvironment to be taken up by CLL cells for GSH synthesis. The elevated GSH in CLL cells in the presence of bone marrow stromal cells significantly protected the leukemia cells from stress-induced apoptosis, and rendered them resistant to standard therapeutic agents such as fludarabine and oxaliplatin. Importantly, disabling of this protective mechanism by depletion of cellular GSH using a pharmacological approach potently sensitized CLL cells to drug treatment, and effectively enhanced the cytotoxic action of fludarabine and oxaliplatin against CLL in the presence of stromal cells. This study reveals a key biochemical mechanism of leukemia-stromal cells interaction, and identifies a new therapeutic strategy to overcome drug resistance in vivo.

Involvement of human chromosome 17 in the control of the metastatic phenotype in melanoma

Fusion of nonmetastatic murine melanoma K1735 C19H cells with metastatic human melanoma A375 C15N cells resulted in a hybrid (termed H7) which was highly metastatic in a nude mouse model. The H7 hybrid retained chromosome 17 as the sole intact human chromosome in the cell. A lung bioassay showed that the K1735 C19H cells were present in the lungs of nude mice with s.c. tumors, yet at 6-weeks after tumor resection, no cells remained in the lung and therefore did not form lung metastases. Examination of various phenotypic properties such as in vivo and in vitro growth demonstrated that phenotypically the H7 hybrid was most like the K1735 C19H cell line except for its metastatic ability. In contrast the H7 hybrid cells containing single or multiple copies of human chromosome 17 with a point mutation at codon 249 (arg-gly) of the p53 gene, readily formed lung metastases. A plasmid containing the human p53 from the H7 hybrid and four other contructs with mutations at codon 143 (val-arg), 175 (arg-his), 249 (arg-ser) and 273 (arg-his) were transfected into K1735 C19H cells. K1735 C19H cells expressing human p53 genes with mutations at codons 249, both the arg-ser mutation and the mutation from the H7 hybrid and 273 produced significantly more lung metastases.^ In vitro assays demonstrated that responses to various cytotoxic and DNA damaging agents varied with the presence of mutant p53 and with the type of agent used. When cultured in mouse lung-conditioned medium, the K1735 C19H cell line was growth-inhibited, while cells containing a mutant human p53 (either on the whole chromosome 17, as in the H7 hybrid cells or from a stably transfected construct) were growth stimulated. Western blot analysis of lung-conditioned media derived from either 6-month or 15-month old mice has detected high levels of soluble Fas ligand in the medium from older animals. Comparison of the levels of Fas receptor on the K1735 C19H cell line and the H7 hybrid were almost identical, but 50% of the K1735 C19H cells were killed in the presence of anti-Fas antibody as opposed to 7% of the H7 hybrid cells. The growth-inhibitory effects of the lung-conditioned medium on the K1735 C19H cells were abrogated by coculture with Fas-Fc, which competes with the Fas ligand for receptor binding. Growth-inhibition of the K1735 C19H was 54% when cultured in 60 $\mu$g/0.2 ml lung-conditioned medium and a control Fc, with only 9% inhibition in 60 $\mu$g/0.2 ml lung-conditioned medium and Fas-Fc. Growth of the H7 cells and K1735 C19H cells transfected with various mutant human p53 genes were unchanged by the presence of either the control Fc or the Fas-Fc. This indicates that the presence of human chromosome 17, and mutant p53 in part protects the cells from Fas:Fas ligand induced apoptosis, and allows the growth of lung metastases. ^

Complement dependent early immunological responses during ex vivo xenoperfusion of hCD46/HLA-E double transgenic pig forelimbs with human blood.

BACKGROUND Besides α1,3-galactosyltransferase gene (GGTA1) knockout, several transgene combinations to prevent pig-to-human xenograft rejection are currently being investigated. In this study, the potential of combined overexpression of human CD46 and HLA-E to prevent complement- and NK-cell-mediated xenograft rejection was tested in an ex vivo pig-to-human xenoperfusion model. METHODS α1,3-Galactosyltransferase knockout heterozygous, hCD46/HLA-E double transgenic (transgenic) as well as wild-type pig forelimbs were ex vivo perfused with whole, heparinized human and autologous pig blood, respectively. Blood samples were analyzed for the production of porcine and/or human inflammatory cytokines as well as complement activation products. Biopsy samples were examined for deposition of human and porcine C3b/c, C4b/c, and C6 as well as CD62E (E-selectin) and CD106 (VCAM-1) expression. Apoptosis was measured in the porcine muscle tissue using TUNEL assays. Finally, the formation of thrombin-antithrombin (TAT) complexes was measured in EDTA plasma samples. RESULTS No hyperacute rejection was seen in this model. Extremity perfusions lasted for up to 12 h without increase in vascular resistance and were terminated due to continuous small blood losses. Plasma levels of porcine cytokines IL1β, IL-6, IL-8, IL-10, TNF-α, and MCP-1 as well as human complement activation markers C3a (P = 0.0002), C5a (P = 0.004), and soluble C5b-9 (P = 0.03) were lower in blood perfused through transgenic as compared to wild-type limbs. Human C3b/c, C4b/c, and C6 as well as CD62E and CD106 were deposited in tissue of wild-type limbs, but significantly lower levels (P < 0.0001) of C3b/c, C4b/c, and C6 deposition as well as CD62E and CD106 expression were detected in transgenic limbs perfused with human blood. Transgenic porcine tissue was protected from xenoperfusion-induced apoptosis (P < 0.0001). Finally, TAT levels were significantly lower (P < 0.0001) in transgenic limb as compared to wild-type limb xenoperfusions. CONCLUSION Transgenic hCD46/HLA-E expression clearly reduced humoral xenoresponses since all, the terminal pathway of complement activation, endothelial cell activation, muscle cell apoptosis, inflammatory cytokine production, as well as coagulation activation, were all downregulated. Overall, this model represents a useful tool to study early immunological responses during pig-to-human vascularized xenotransplantation in the absence of hyperacute rejection.

Ceramide kinase contributes to proliferation but not to prostaglandin E2 formation in renal mesangial cells and fibroblasts

Background/Aims: Ceramide kinase (CerK) catalyzes the generation of the sphingolipid ceramide-1-phosphate (C1P) which regulates various cellular functions including cell growth and death, and inflammation. Here, we used a novel catalytic inhibitor of CerK, NVP-231, and CerK knockout cells to investigate the contribution of CerK to proliferation and inflammation in renal mesangial cells and fibroblasts. Methods: Cells were treated with NVP-231 and [3H]-thymidine incorporation into DNA, [3H]-arachidonic acid release, prostaglandin E2 (PGE2) synthesis, cell cycle distribution, and apoptosis were determined. Results: Treatment of rat mesangial cells and mouse renal fibroblasts with NVP-231 decreased DNA synthesis, but not of agonist-stimulated arachidonic acid release or PGE2 synthesis. Similarly, proliferation but not arachidonic acid release or PGE2 synthesis was reduced in CERK knockout renal fibroblasts. The anti-proliferative effect of NVP-231 on mesangial cells was due to M phase arrest as determined using the mitosis markers phospho-histone H3, cdc2 and polo-like kinase-1, and induction of apoptosis. Moreover, loss of CerK sensitized cells towards stress-induced apoptosis. Conclusions: Our data demonstrate that CerK induces proliferation but not PGE2 formation of renal mesangial cells and fibroblasts, and suggest that targeted CerK inhibition has potential for treating mesangioproliferative kidney diseases.

The ceramide kinase inhibitor NVP-231 inhibits breast and lung cancer cell proliferation by inducing M phase arrest and subsequent cell death

Background and Purpose Ceramide kinase (CerK) catalyzes the generation of ceramide-1-phosphate which may regulate various cellular functions, including inflammatory reactions and cell growth. Here, we studied the effect of a recently developed CerK inhibitor, NVP-231, on cancer cell proliferation and viability and investigated the role of cell cycle regulators implicated in these responses. Experimental Approach The breast and lung cancer cell lines MCF-7 and NCI-H358 were treated with increasing concentrations of NVP-231 and DNA synthesis, colony formation and cell death were determined. Flow cytometry was performed to analyse cell cycle distribution of cells and Western blot analysis was used to detect changes in cell cycle regulator expression and activation. Key Results In both cell lines, NVP-231 concentration-dependently reduced cell viability, DNA synthesis and colony formation. Moreover it induced apoptosis, as measured by increased DNA fragmentation and caspase-3 and caspase-9 cleavage. Cell cycle analysis revealed that NVP-231 decreased the number of cells in S phase and induced M phase arrest with an increased mitotic index, as determined by increased histone H3 phosphorylation. The effect on the cell cycle was even more pronounced when NVP-231 treatment was combined with staurosporine. Finally, overexpression of CerK protected, whereas down-regulation of CerK with siRNA sensitized, cells for staurosporine-induced apoptosis. Conclusions and Implications Our data demonstrate for the first time a crucial role for CerK in the M phase control in cancer cells and suggest its targeted inhibition, using drugs such as NVP-231, in combination with conventional pro-apoptotic chemotherapy.

Assessment of tumor regression of esophageal adenocarcinomas after neoadjuvant chemotherapy: comparison of 2 commonly used scoring approaches.

Histopathologic determination of tumor regression provides important prognostic information for locally advanced gastroesophageal carcinomas after neoadjuvant treatment. Regression grading systems mostly refer to the amount of therapy-induced fibrosis in relation to residual tumor or the estimated percentage of residual tumor in relation to the former tumor site. Although these methods are generally accepted, currently there is no common standard for reporting tumor regression in gastroesophageal cancers. We compared the application of these 2 major principles for assessment of tumor regression: hematoxylin and eosin-stained slides from 89 resection specimens of esophageal adenocarcinomas following neoadjuvant chemotherapy were independently reviewed by 3 pathologists from different institutions. Tumor regression was determined by the 5-tiered Mandard system (fibrosis/tumor relation) and the 4-tiered Becker system (residual tumor in %). Interobserver agreement for the Becker system showed better weighted κ values compared with the Mandard system (0.78 vs. 0.62). Evaluation of the whole embedded tumor site showed improved results (Becker: 0.83; Mandard: 0.73) as compared with only 1 representative slide (Becker: 0.68; Mandard: 0.71). Modification into simplified 3-tiered systems showed comparable interobserver agreement but better prognostic stratification for both systems (log rank Becker: P=0.015; Mandard P=0.03), with independent prognostic impact for overall survival (modified Becker: P=0.011, hazard ratio=3.07; modified Mandard: P=0.023, hazard ratio=2.72). In conclusion, both systems provide substantial to excellent interobserver agreement for estimation of tumor regression after neoadjuvant chemotherapy in esophageal adenocarcinomas. A simple 3-tiered system with the estimation of residual tumor in % (complete regression/1% to 50% residual tumor/>50% residual tumor) maintains the highest reproducibility and prognostic value.

Subunit composition of VRAC channels determines substrate specificity and cellular resistance to Pt-based anti-cancer drugs

Although platinum-based drugs are widely used chemotherapeutics for cancer treatment, the determinants of tumor cell responsiveness remain poorly understood. We show that the loss of subunits LRRC8A and LRRC8D of the heteromeric LRRC8 volume-regulated anion channels (VRACs) increased resistance to clinically relevant cisplatin/carboplatin concentrations. Under isotonic conditions, about 50% of cisplatin uptake depended on LRRC8A and LRRC8D, but neither on LRRC8C nor on LRRC8E. Cell swelling strongly enhanced LRRC8-dependent cisplatin uptake, bolstering the notion that cisplatin enters cells through VRAC. LRRC8A disruption also suppressed drug-induced apoptosis independently from drug uptake, possibly by impairing VRAC-dependent apoptotic cell volume decrease. Hence, by mediating cisplatin uptake and facilitating apoptosis, VRAC plays a dual role in the cellular drug response. Incorporation of the LRRC8D subunit into VRAC substantially increased its permeability for cisplatin and the cellular osmolyte taurine, indicating that LRRC8 proteins form the channel pore. Our work suggests that LRRC8D-containing VRACs are crucial for cell volume regulation by an important organic osmolyte and may influence cisplatin/carboplatin responsiveness of tumors.

Emodin, a tyrosine kinase inhibitor, and human cancer

Many human diseases, including cancers, result from aberrations of signal transduction pathways. The recent understanding of the molecular biochemistry of signal transduction in normal and transformed cells enable us to have a better insight about cancer and design new drugs to target this abnormal signaling in the cancer cells. Tyrosine kinase pathway plays a very important role in normal and cancer cells. Enhanced activity of tyrosine kinases has been associated with many human cancer types. Therefore, identifying the type of tyrosine kinases involved in a particular cancer type and blocking these tyrosine kinase pathways may provide a way to treat cancer. Receptor tyrosine kinase expression, namely epidermal growth factor receptor (EGFR) family, was examined in the oral squamous cell carcinoma patients. The expression levels of different members of the EGFR family were found to be significantly associated with shorter patients' survival. Combining EGFR, HER-2/neu, and HER-3 expression can significantly improve the predicting power. The effect of emodin, a tyrosine kinase inhibitor, on these receptors in head and neck squamous cell carcinoma cell lines was examined. Emodin was found to suppress the tyrosine phosphorylation of HER-2/neu and EGF-induced tyrosine phosphorylation of EGFR. Emodin also induced apoptosis and downregulated the expression of anti-apoptotic protein bcl-2 in oral squamous cell carcinoma cells. It is known that tyrosine kinase pathways are involved in estrogen receptor signaling pathway. Therefore, the effects of inhibiting the tyrosine kinase pathway in estrogen receptor-positive breast cancers was studied. Emodin was found to act similarly to antiestrogens, capable of inhibiting estrogen-stimulated growth and DNA synthesis, and the phosphorylation of Rb protein. Interestingly, emodin, and other tyrosine kinase inhibitors, such as RG 13022 and genistein, depleted cellular levels of estrogen receptor protein. Emodin-induced depletion of estrogen receptor was mediated by the proteasome degradation pathway. In summary, we have demonstrated that tyrosine kinase pathways play an important role in oral squamous cell carcinoma and estrogen receptor-positive breast cancer. Targeting the tyrosine kinases by inhibitors, such as emodin, may provide a potential way to treat the cancer patients. ^

Characterization of E2F1's oncogenic, apoptotic and tumor-suppressive activities utilizing the K5 mouse model

Though E2F1 is deregulated in most human cancers by mutations of the p16-cyclin D-Rb pathway, it also exhibits tumor suppressive activity. A transgenic mouse model overexpressing E2F1 under the control of the bovine keratin 5 (K5) promoter exhibits epidermal hyperplasia and spontaneously develops tumors in the skin and other epithelial tissues after one year of age. In a p53-deficient background, aberrant apoptosis in K5 E2F1 transgenic epidermis is reduced and tumorigenesis is accelerated. In sharp contrast, K5 E2F1 transgenic mice are resistant to papilloma formation in the DMBA/TPA two-stage carcinogenesis protocol. K5 E2F4 and K5 DP1 transgenic mice were also characterized and both display epidermal hyperplasia but do not develop spontaneous tumors even in cooperation with p53 deficiency. These transgenic mice do not have increased levels of apoptosis in their skin and are more susceptible to papilloma formation in the two-stage carcinogenesis model. These studies show that deregulated proliferation does not necessarily lead to tumor formation and that the ability to suppress skin carcinogenesis is unique to E2F1. E2F1 can also suppress skin carcinogenesis when okadaic acid is used as the tumor promoter and when a pre-initiated mouse model is used, demonstrating that E2F1's tumor suppressive activity is not specific for TPA and occurs at the promotion stage. E2F1 was thought to induce p53-dependent apoptosis through upregulation of p19ARF tumor suppressor, which inhibits mdm2-mediated p53 degradation. Consistent with in vitro studies, the overexpression of E2F1 in mouse skin results in the transcriptional activation of the p19ARF and the accumulation of p53. Inactivation of either p19ARF or p53 restores the sensitivity of K5 E2F1 transgenic mice to DMBA/TPA carcinogenesis, demonstrating that an intact p19ARF-p53 pathway is necessary for E2F1 to suppress carcinogenesis. Surprisingly, while p53 is required for E2F1 to induce apoptosis in mouse skin, p19ARF is not, and inactivation of p19ARF actually enhances E2F1-induced apoptosis and proliferation in transgenic epidermis. This indicates that ARF is important for E2F1-induced tumor suppression but not apoptosis. Senescence is another potential mechanism of tumor suppression that involves p53 and p19ARF. K5 E2F1 transgenic mice initiated with DMBA and treated with TPA show an increased number of senescence cells in their epidermis. These experiments demonstrate that E2F1's unique tumor suppressive activity in two-stage skin carcinogenesis can be genetically separated from E2F1-induced apoptosis and suggest that senescence utilizing the p19ARF-p53 pathway plays a role in tumor suppression by E2F1. ^

14-3-3zeta overexpression in multiple human cancers plays a critical role in cancer progression

14-3-3 is a family of highly conserved and ubiquitously expressed proteins in eukaryotic organisms. 14-3-3 isoforms bind in a phospho-serine/threonine-dependent manner to a host of proteins involved in essential cellular processes including cell cycle, signal transduction and apoptosis. We fortuitously discovered 14-3-3 zeta overexpression in many human primary cancers, such as breast, lung, and sarcoma, and in a majority of cancer cell lines. To determine 14-3-3 zeta involvement in breast cancer progression, we used immunohistochemical analysis to examine 14-3-3 zeta expression in human primary invasive breast carcinomas. High 14-3-3 zeta expression was significantly correlated with poor prognosis of breast cancer patients. Increased expression of 14-3-3 zeta was also significantly correlated with elevated PKB/Akt activation in patient samples. Thus, 14-3-3 zeta is a marker of poor prognosis in breast cancers. Furthermore, up-regulation of 14-3-3 zeta enhanced malignant transformation of cancer cells in vitro. ^ To determine the biological significance of 14-3-3 zeta in human cancers, small interfering RNAs (siRNA) were used to specifically block 14-3-3 zeta expression in cancer cells. 14-3-3 zeta siRNA inhibited cellular proliferation by inducing a G1 arrest associated with up-regulation of p27 KIP1 and p21CIP1 cyclin dependent kinase inhibitors. Reduced 14-3-3 zeta inhibited PKB/Akt activation while stimulating the p38 signaling pathway. Silencing 14-3-3 zeta expression also increased stress-induced apoptosis by caspase activation. Notably, 14-3-3 zeta siRNA inhibited transformation related properties of breast cancer cells in vitro and inhibited tumor progression of breast cancer cells in vivo. 14-3-3 zeta may be a key regulatory factor controlling multiple signaling pathways leading to tumor progression. ^ The data indicate 14-3-3 zeta is a major regulator of cell growth and apoptosis and may play a critical role in the development of multiple cancer types. Hence, blocking 14-3-3 zeta may be a promising therapeutic approach for numerous cancers. ^